RC Motor Controllers
Bill Chennault
Posts: 1,198
All--
Will you please tell me the differences between a remote control motor controller--such as the high amperage motor controllers used in combat 'bots--and the motor controllers we commonly discuss? And, is it possible to use a high-amp RC motor controller in a machine we might consider, in other words, not a remote controlled device, but something autonomous, perhaps controlled by a Stamp?
Thanks!
--Bill
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You are what you write.
Will you please tell me the differences between a remote control motor controller--such as the high amperage motor controllers used in combat 'bots--and the motor controllers we commonly discuss? And, is it possible to use a high-amp RC motor controller in a machine we might consider, in other words, not a remote controlled device, but something autonomous, perhaps controlled by a Stamp?
Thanks!
--Bill
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You are what you write.
Comments
I'm not quite sure which "motor controllers we discuss" as there are many different discussion about all sorts of motor controller boards. Perhaps some basics are in order first, and then some detailed information.
All motor control boards (MCB's) that are usually discussed here perform some of the similar functions. They all enable the user to control the speed and/or direction of one or more DC motors. They generally offload direct control of the motors to an offboard PCB which may be "intelligent" or "dumb" as the case may be. The MCB may also control more than one motor. Some can control up to 16 to 32 motors of the R/C servo type.
The DC motors being controlled may be one of several types:
· DC, R/C servo motors (normal type or those modified for continuous rotation)
· DC, permanent magnet, brushed motors
· DC, stepper motors (uni-polar or bi-polar configurations)
Beyond that are matters of voltage and amperage. MCB's may operate at completely different voltages than the base processor (computer or micro-processor). While the base processor may be limited to 5-12 volts DC, some MCB's can handle DC motors up to 90-130 volts. More common are those which operate at R/C servo levels (6.0 VDC - 9.6 VDC) or in the 12-48 VDC range. The latter represent wheelchair motors and the like.
MCB's intended for smaller DC motors may be limited to 2-6 amps or less, but the larger units can handle 50 amps and beyond. There are also some mid-range offerings like the Parallax HB-25 which weighs in at 25 amps, and fills a very common gap between small and large MCB's. The HB-25 drives R/C servos motors, and can handle up to two motors if daisy chained.
Nearly all MCB's designed for use with DC PM and DC stepper motors use some sort of H-bridge to control the motors. This provides both speed control, and reversing. Depending on the MCB it may also provide braking.
Above and beyond that, some MCB's have specialized facilities. Some can be given a series of instructions, and the instructions can be "replayed" at some future time. Some MCB's will provide automatic ramping (acceleration and de-acceleration), braking, dynamic braking, and also possibly feedback to the base processor. It goes without saying the more features a given MCB has, generally the more they cost.
If this didn't answer your question, perhaps you can now be a bit more specific, now that this much has been exposed. The only "dumb" question is the one that isn't asked
Regards,
Bruce Bates
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Post Edited (Bruce Bates) : 1/16/2008 4:22:31 AM GMT
Thank you very much for taking the time to write that reply!
I have many motor controllers. Some are from Parallax and some are from other vendors, such as Poulou (sp?). All of them allow me to control small DC motors easily with a Stamp. The HB-25 is my current favorite because it will handle up to 25 amps which means I can use my 42 amp stall current motors with the HB-25 as long as I don't exceed the capacity of the HB-25. (I am not sure what happens if I DO exceed the capacity of the HB-25. Do you know?)
I understand there are motor controllers that will handle far more current. My question is--cost aside (for the moment!)--are they as compatible with the digital world, essentially the Stamp, as the HB-25 and other Parallax and Poulou motor controllers? Another question concerns the difference between the high-amperage motor controllers used in the radio controlled battle 'bots and those we "commonly discuss" on this forum. Is it feasible to interface such a high-amp device to something like a Stamp?
I appreciate your help.
--Bill
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You are what you write.
If you exceed 25 amps with the HB-25, that cute little automotive type fuse will die valiently saving your HB-25 from total destruction. Replace the 25 amp fuse, and off you go again. No "magic smoke" was lost in this process!
I'm not quite sure what you mean by "compatible with the digital world". Just by way of example, the HB-25 accepts pulses which could just as easily be produced by analog means as digital means. The means are really insignificant to the task IMHO, unless I'm mis-understaning your question.
Almost any MCB can be interfaced with the PBASIC Stamp so long as it accepts one of the following interfaces: asynchrous serial (SERIN/SEROUT), synchrounous serial (SHIFTIN/SHIFTOUT), pulse instruction (PULSOUT), or PWM (PWM). The Stamp can also interface with "dumb" direct-wire protocals as well (HIGH/LOW).
I hope that helps. BTW, I love MCB's which may be apparent
Regards,
Bruce Bates
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Veni, Vidi, Velcro! - I came, I saw, I stuck around!
What I REALLY meant was that I was ignorant! But, I have read quite a bit and am now less ignorant. I thought that RC motor controllers were completely different than the devices we hook up to Stamps. The ones I have just finished reading about appear to be far more capable with several interface options, including RS-232.
I just spent the last hour or so reading the Roboteq site. They have some real MCBs! As long as money is no object. (Do you have a hint concerning Roboteq-similar, but less expensive MCBs?)
Thanks for all your help. I needed it and will continue to need it!
--Bill
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You are what you write.
If you hook a big motor to an RC controller, and then hook your Stamp to the controller, treat it just like a big continuous rotation servo. 1.0ms pulse will be full reverse, 1.5ms pulse will be stopped, 2.0ms will be full forward (usually).
Controllers designed for a host often include one or several communications protocols (say serial or I2C) and often have more features -- like on-board ramping, or checking battery voltage, or inertial settings or whatever. Many of these kinds of boards often ALSO include the ability to use RC pulses (again, turning the motor into a virtual servo).
For example, the dual MD22 I use in my big 'bot does 10A per motor peak, can be run either via I2C or RC pulses. In I2C mode I can send motor speeds, read motor speeds, set ramp values, set turn/diff modes, etc. In RC mode I can send motor speeds, but that's it.
The HB25 by Parallax is, essentially, an RC controller -- it's designed to receive standard RC pulse widths.
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Thanks . . . I am understanding more and more. I believe that this Roboteq 50 amp controller is much like the HB-25, but I am not sure it is "fire and forget" like the HB-25.
I think the schematics they posted are somewhat dated and do not precisely fit my desires, anyway. I have their permission to post their drawings here for help by forum members and Parallax (should they be so kind). I'll post the drawing when I get a moment, but it is at the site I included above.
They show +12vdc to Vin and I know they mean +5vdc. What I don't know (other than the fire and forget issue) is what happens to the rest of the circuit if I change their PWR (Vin) to +5vdc. I would also like to get rid of the mechanical relay and go with an SSR. The demo software uses Pbasic's PWM instruction, so I GUESS there is no fire and forget feature ala HB-25.
(The drawing is actually of their 24 volt, 30 amp MCB, but they told me the connections were the same as the 50 amp, MCIPC-50A.)
Doesn't "Parallax HB-50" sound just great? I really like the ring of it. I'll say it again: Parallax HB-50.
--Bill
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You are what you write.
Most of the RC type H-Bridge controllers out there like the Roboteq or the ones made by Vantec, etc will expect to keep seeing a servo style pulse on a regular interval. You could probably use one of the SX28 chips to "offload" that task to make any standard RC or RC style H-Bridge controller act similar to what you expect the HB-25 to do.
Does that help?
Robert
Some of their circuit is flair -- for example, the transistor/diode relay driver is just a "Stamp-controllable power switch". You could eliminate that and just have a heavy duty toggle switch. The other part of the circuit from the Stamp pin to the controller input is for conditioning PWM.
And I believe you are right, this would not be set it and forget it -- though it was unclear from their page. This may be more of a "driver" -- the PWM and amp -- many motor "controllers" have the amp circuitry tied to some kind of small micro (like a Pic or SX) -- the small micro generates PWM for the driver and handles communication with the host (freeing the host to do other things).
I've seen others comment that the Roboteq drivers are really good and solid for very high amperages. Beyond that I can't say.
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When the going gets weird, the weird turn pro. -- HST
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Robert, hmmm. Yes, I can see how using the SX as a front end to the motor controller to make it behave like an HB-25 might be a rather straight-forward proposition. In fact, an SX dedicated to the task could doubtless handle more motor controllers than I can buy. Plus, if I WANTED to, I could create my own instruction set for the SX/MCB. I did that with Ugly Buster. The slave Stamps understand about 30 fixed length, non-Pbasic instructions; stop, various speeds, forward, reverse, and make all ports inputs.
Poor Ugly Buster is languishing while I work on my gearmotor-driven joint transmission. It is within about two hours of completion. I just have to create a couple of motor mount plates. The joint transmission is the first component of a walker I want to construct. Guess what microcontroller will drive the walker? (Probably several of them.)
Zoot, you are correct: The Roboteq MCB line is not "fire and forget." And, instead of a heavy duty toggle switch I will see if there is a Futurlec SSR I can use. They are elegant solutions. Ugly Buster has one, rated at 40 amps, switching the 12 volt, 24 amp-hour system on and off under program control by the BS2p40 master.
--Bill
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You are what you write.
The remote is communicating with an on-board "reciever" unit. The "reciever" takes the repetitive signals from the remote, breaks out the different channels signals, and routes those to discrete outputs on the "reciever". These outputs then have the 'classic' three-pin Servo connector plugged in to them, which provide power, signal, and ground to the connected devices -- position Servo's, Continuous Rotation PWM devices like the HB-25, and Electronic Speed Control (ESC) devices.
The signal on the 'signal' pins is (I believe) ALWAYS the "1 mSec to 2 mSec pulse indicating position, repeat every 20 mSec to 50 mSec" "Servo Control Pulse". This signal is used for Electronic Speed Control (ESC) for "Stop to Full Speed". For continuous rotation things like wheels, a 1.5 mSec 'pulse' indicates 'STOP', while 1 mSec pulse means "full speed one way" and 2 mSec means "full speed the other way".
So I believe that IS the "Common Interface" you're referring to. LOTS of vendors have built equipment for this, and I assume the really expensive "FULL POWER" stuff also uses this signal interface. The POWER interface (the multiple amps and DC volts controlled, and torque generated) can become quite large and beefy, but the signal interface remains the same.
As i am too in educational mode, and probably will be forever, i am always interested in digging up some dirt, as " does this really have to be so complicated ? " So, after doing the usual looking at a gazillion or 2 search results, here is what i found. First, the HB25 can take a surge current of 35 amps, maybe not long, which is close to what you need, a larger heat-sink may get you more. The Hb25 is not magic, it is basically a speed controller with a pwm coprocessor, which is why it is easy to use. The battlebot controllers are all run by RC, other interface options are available on some, but that is the way they are designed, which is just servo radio control or basically pwm input. Nutshell
You can use the large amp controllers, but to run it from a stamp, pwm input is required which the stamp is time restricted on, so a pwmpal or servopal would be the way to go. The pwmpal has counter inputs which may be useful. So there you have the motor driver and pwm coprocessor, same as a HB25. If anyone cares to differ on this, i would be interested to find out why? If you are running a big bot, you need the power to go with it. I realize they are not cheap, but there are some reasonably priced ones out there. Some have dual motor control which can be a little better for cost. This is a pretty good site, make sure the controllers will do what you want if you are interested.
www.robotmarketplace.com/products/speed_controllers_main.html
Or an SX for $2.79. Jon Williams even had an article in N/V late Fall with code for a dual motor controller (two PWM outs into an H-bridge). Plus you'd get a bunch of extro I/O pins to use as an I/O expander, or build motor encoding into the same SX.
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When the going gets weird, the weird turn pro. -- HST
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Sarcasm aside, i was answering the original question, if someone proposes to use a sx, they should at least provide the actual cost of hardware, not just the chip.
.1uf cap = .10
a few resistors = .25
4-pin programming header = .25 (or less if you just strip one off any old techno junk you have lying around)
The issue w/r/t cost if you are rolling your own is the H-bridge/amp itself -- Jon's article used a single IC motor driver which retails for around 1.79, but that's for driving toy motors at < 500ma.
I was mostly referring to building the equivalent of the PWMPal or ServoPal for a few dollars. Since both those products presume regulated 5v, you don't really have too many other parts than the ones listed above. If you need 5v regulation, add another $2 or so for regulator, heatsink, caps.
I think the PWMpal is a great product -- it's just a bit pricey if you are adding that on top of a $70-$150 high-amp driver. By the same token, what's your time worth compared to having something "ready to go".
See NV144 -- if you were using the SX to drive an h-bridge, or whatever, you just need the code and the SX, not the driver and protoboard and such.
I know you are being tongue-and-cheek, but you know what? That really has been *my* experience anyway. It's like magic -- hardly any external components for the SX, dump some code, everything works. Of course, that's using code tested and proven by others -- when you start writing your own, that's when the hours stack up
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When the going gets weird, the weird turn pro. -- HST
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If you want to honestly consider an SX solution, one needs to add in the cost of the hardware programmer. That's $29.95 for the SX Blitz, or $49.95 for the SX Key. If you then want to amortize the cost of the hardware programmer over (say) 100 units, that's fine.
After all, I doubt you'd permit a raw cost PIC solution and not consider the hardware programmer. Interestingly, that's one of the costs one DOESN'T have to bear when using the PBASIC Stamp.
Fair is fair.
Regards,
Bruce Bates
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Veni, Vidi, Velcro! - I came, I saw, I stuck around!
Bruce is correct with the start-up cost, is it worth the time and effort over a pre-built solution at this point?
Post Edited (kelvin james) : 1/19/2008 5:21:45 AM GMT
The Stamps and SXes are apples and oranges, of course. But for something like this, the SX is perfect; esp with Stamp(s) as host(s). And if the ServoPal is $30, and a PSC is $40, if you just replicate those two devices, the Key easily pays for itself.
Part of why I brought it up is that Bill has been poking around in the SX threads as well, if I remember, and his networked Stamp setup is suited to the SX for peripherals. Might be the impetus to take the plunge, esp. because the motor controller code in N/V could be run for this purpose without modification, and SX/B right now is extremly similar to Pbasic. Bill -- you have what? a regular Stamp plus 5 OEMs? That would be like $210 in Stamps? Nice.
In any case, to come full circle -- Bill have you checked out Devantech's high amp motor controllers? They're plug-n-play and might do what you need. Not in the 75-100amp range, though, more like 20-30amps running and perhaps double that for short-term stall (but they do a faded powerdown in over-current or over-temp conditions).
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When the going gets weird, the weird turn pro. -- HST
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www.ifirobotics.com/speed-controller-selection-guide.shtml
·You can use the standard servo pulses to control the speed. also if you like the stamp you can build a simple 556 based servo exerciser with a digital pot.
I attached a schematic of a BS2 and 556 controlling a servo pulse.
You can use the same CLK and U/D pins to drive multi AD5220s and just add a new BS2 pin to each CS pin on the
AD5220s and then select which one to control then set the position then move the next one.
hope this·helps and as far as cost goes...
AD5220··· $2.20
LM556········ .48
discretes·····.50
Total·······$3.18 each channel of control.
Zoot, you bet I'm listening! Thanks! I also have two of Robert's SX 40 pin module kits. (I have been too busy to put them together.) I am also going to buy the Parallax SX Controller Board when they provide it with the USB programming module, which should be towards the end of the month, I think.
bennettdan, thanks for the link and the schematic. I will study both.
--Bill
ps By the way, Robert's kits are very, VERY professional.
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You are what you write.
bennettdan -- cool circuit. And those high-amp drivers look really nice. I might check those out for my next project -- a huge garden-bot.
I'll still make the case for doing servo control with an SX or similar -- barring one-time cost of the key, instead of 3.18 per channel, it's about $4 total -- and you can run 8-16 servos off the one chip with only three or four external parts. And a single serial pin on the host (a pin that can be shared with any other open-true serial devices on the same line that allow for an address header).
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When the going gets weird, the weird turn pro. -- HST
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I'm really confused about the motor speed controllers vs. "ESC's" that are for brushless motors.· I understand the difference between the two motors, but not why there are different speed controllers.·
My ultimate goal is to find a motor speed controller·for a brushed motor that·can handle the range (amps/volts) of the HB-25, but is less bulky.· Like the Pololu micro, but for more amps. ·Everytime I find websites with these motor speed controllers, most of the ideal one's are ESC's for brushless, or they don't clarify if they work on brushed motors, so I'm hesitant to buy.
thanks.
·
I also like the SX for servo/ESC control and many other projects if you dont care to learn how to program them.
Bill the 883 speed controllers are very nice.
J.T. check out this sight they have a few brushed ESC at the bottom but you cant use a brushless ESC with a brushed motor as far as I know.
www3.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=esc
It's an SX based servo and LED controller (could also be used for any "RC-ready" motor controller) that is commanded by a host (e.g. Stamp) via serial comm.
Total cost was just under $7 -- including everything except the SX-Key (and I've cranked out so many SX projects and peripherals over the last six months that it hardly counts, to be honest -- I prob. spent more on solder and wire).
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When the going gets weird, the weird turn pro. -- HST
1uffakind.com/robots/povBitMapBuilder.php
1uffakind.com/robots/resistorLadder.php